In addition to the comparisons that some here can offer (and the many that are available by searching, try this thread in particular: Portaphile V2 Owners Thread
), you should definitely ask Cesar (the maker of the Portaphile amps) to explain the differences between the V1, V2, and (the current model) the V2^2. He is very responsive & helpful. I picked up a V2 from the bargains page, and like it a lot, but you should ask Cesar to describe some of the differences to you, and in particular ask him about how those changes might be perceived with the headphones you will be using. Also, you might try to PM Romanee. He has auditioned a bunch of amps including every portaphile as far as I can tell. From his posts, he should be able to offer useful descriptions of some of the differences, and maybe make some recommendations to you.